The present invention relates to an overhead wire tensioning device that can be used for such applications as maintaining a tension of overhead wire for railways.
Overhead wire, in particular overhead wire for railways (such as main wire, support wire and trolley lines), is required to be tensioned appropriately at all times because the tension of the overhead wire is affected by such factors as the elongation and shrinking due to temperature changes, elongation due to creeping and wear of the material of the wire, and the tilting of the supporting structures over time. It is particularly desirable to be able to automatically adjust the tension of the overhead wire, and eliminate the need for maintenance work.
Conventionally known automatic tensioning devices for maintaining the tension of overhead wire at a constant level include those using pulleys to produce a tension from the gravitational force acting on a weight, and those using springs to produce a tension from the spring force of a spring. The pulley type can provide a favorable performance in maintaining the tension at a constant level, but the work involved in installation is significant and a regular maintenance work is required to prevent degradation of the wire. Tensioning devices using gas springs (such as those disclosed in Japanese patent laid open publication No. 6-16068) have drawn attention in this regard as they allow the entire assembly to be highly compact and light-weight, and eliminate the need for constant maintenance work.
A gas spring type tensioning device of this type includes a cylinder case defining a gas chamber and having one end of the device attached to one of a fixed end and the overhead wire, and a cylinder rod extending out of the cylinder case and having an end attached to the other of the fixed end and the overhead wire. As the cylinder rod and the cylinder case is required to be axially slidable relative to each other, if the mechanism for permitting this relative sliding movement fails to operate properly, the sliding resistance between them could increase to such an extent that a desired tension may not be achieved. Therefore, it has been desired to improve the device so as to eliminate such a possibility.
A gas spring type tensioning device of this type additionally includes a tension rod extending between the cylinder and the overhead wire and having an end pivotally attached to the cylinder via a trunnion shaft to accommodate the swaying movement of the overhead wire. If such a pivotable arrangement fails, this tension rod mechanism becomes unable to accommodate the swaying movement of the overhead wire, and this likewise may prevent maintenance of a desired tension.
In view of such problems of the prior art, a primary object of the present invention is to provide an overhead wire tensioning device which can favorably maintain a tension of overhead wire at a constant level, and is highly reliable in use without requiring any constant maintenance work.
Other features and advantages of the present invention will be described in the following with reference to the appended drawings.